(ethylene, vinyl acetal) copolymers and their use in lithographic printing plate precursors

ABSTRACT

A copolymer includes (i) a plurality of ethylenic moieties A having a structure according to the formula: 
     
       
         
         
             
             
         
       
         
         
           
             wherein R 2  and R 3  independently represent hydrogen, a halogen, an optionally substituted linear, branched, or cyclic alk(en)yl group, or an optionally substituted aromatic or heteroaromatic; (ii) a plurality of acetal moieties B having a structure according to the formula: 
           
         
       
    
     
       
         
         
             
             
         
       
         
         
           
             wherein L 1  represents a divalent linking group, x=0 or 1, and R 1  represents an optionally substituted aromatic or heteroaromatic group including at least one hydroxyl group; and (iii) a plurality of acetal moieties C and/or moieties D which include a structural moiety including a chromophoric group having its main absorption in the infrared region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2015/062514, filed Jun. 4, 2015. This application claims thebenefit of European Application No. 14172254.6, filed Jun. 13, 2014,which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to (ethylene, vinyl acetal) copolymers andto lithographic printing plate precursors including such copolymers.

2. Description of the Related Art

Lithographic printing typically involves the use of a so-called printingmaster such as a printing plate which is mounted on a cylinder of arotary printing press. The master carries a lithographic image on itssurface and a print is obtained by applying ink to said image and thentransferring the ink from the master onto a receiver material, which istypically paper. In conventional lithographic printing, ink as well asan aqueous fountain solution (also called dampening liquid) are suppliedto the lithographic image which consists of oleophilic (or hydrophobic,i.e. ink-accepting, water-repelling) areas as well as hydrophilic (oroleophobic, i.e. water-accepting, ink-repelling) areas. In so-calleddriographic printing, the lithographic image consists of ink-acceptingand ink-adhesive (ink-repelling) areas and during driographic printing,only ink is supplied to the master.

Lithographic printing masters are generally obtained by the image-wiseexposure and processing of an imaging material called plate precursor.The coating of the precursor is exposed image-wise to heat or light,typically by means of a digitally modulated exposure device such as alaser, which triggers a (physico-)chemical process, such as ablation,polymerization, insolubilization by cross-linking of a polymer or byparticle coagulation of a thermoplastic polymer latex, solubilization bythe destruction of intermolecular interactions or by increasing thepenetrability of a development barrier layer. Although some plateprecursors are capable of producing a lithographic image immediatelyafter exposure, the most popular plate precursors require wet processingsince the exposure produces a difference of solubility or of rate ofdissolution in a developer between the exposed and the non-exposed areasof the coating. In positive working plates, the exposed areas of thecoating dissolve in the developer while the non-exposed areas remainresistant to the developer. In negative working plates, the non-exposedareas of the coating dissolve in the developer while the exposed areasremain resistant to the developer. Most plates contain a hydrophobiccoating on a hydrophilic support, so that the areas which remainresistant to the developer define the ink-accepting, printing areas ofthe plate while the hydrophilic support is revealed by the dissolutionof the coating in the developer at the non-printing areas.

Many lithographic printing plates contain polymeric binders such asphenolic resins which can be baked in order to increase the run lengthon the press. Over the last few years, printing plate materials whichprovide a high run length without baking have become more popularbecause the post-bake oven can be eliminated leading to reduced energyconsumption and less floor space. The trend towards higher printingspeeds on web presses and the use of recycled paper require platecoatings that are characterised by a high abrasion resistance. Unbakedphenolic resins such as novolac, resol or poly(vinyl phenol) have a poorabrasion resistance and cannot provide a high run length in suchconditions.

In the prior art, the run length of lithographic printing plates basedon phenolic resins has been improved by chemical modification of suchbinders. Examples thereof are described in for example WO 99/01795, EP934 822, EP 1 072 432, U.S. Pat. No. 3,929,488, EP 2 102 443, EP 2 102444, EP 2 102 445 and EP 2 102 446. Phenolic resins have also been mixedwith or replaced by other polymers such as poly(vinyl acetal) resins inorder to improve the abrasion resistance of the coating. Suitablepoly(vinyl acetal) resins are described in U.S. Pat. No. 5,262,270; U.S.Pat. No. 5,169,897; U.S. Pat. No. 5,534,381; U.S. Pat. No. 6,458,511;U.S. Pat. No. 6,541,181; U.S. Pat. No. 6,087,066; U.S. Pat. No.6,270,938; WO 2001/9682; EP 1 162 209; U.S. Pat. No. 6,596,460; U.S.Pat. No. 6,458,503; U.S. Pat. No. 6,783,913; U.S. Pat. No. 6,818,378;U.S. Pat. No. 6,596,456; WO 2002/73315; WO 2002/96961; WO 2003/79113; WO2004/20484; WO 2004/81662; EP 1 627 732; WO 2007/17162; WO 2008/103258;U.S. Pat. No. 6,255,033; WO 2009/5582; WO 2009/85093; WO 2001/09682; US2009/4599; WO 2009/99518; US 2006/130689; US 2003/166750; U.S. Pat. No.5,330,877; US 2005/3296; WO 2007/3030; US 2009/0291387; US 2010/47723and US 2011/0059399.

Poly(vinyl acetal) resins are prepared in the art by acetalisation ofpoly(vinyl alcohol) with aldehydes. Poly(vinyl acetals) used forlithographic printing plate coatings typically comprise both ahydrophobic acetal moiety, which provides the ink-acceptance, and anhydroxyl substituted aromatic acetal moiety, which produces thesolubility differentiation in an alkaline developer upon exposure.

Such poly(vinyl acetal) resins are typically prepared by theacetalisation of poly(vinyl alcohol) with a mixture of aldehydes, e.g.an aliphatic aldehyde such as butyraldehyde mixed with a phenolicaldehyde such as hydroxybenzaldehyde. The physical and chemicalproperties of such poly(vinyl acetal) resins are highly dependent on thedegree of acetalysation, the ratio of the aliphatic and the aromaticacetal moieties, the stereochemistry and the random or block nature ofthe acetal resin. Small shifts in process conditions during thepreparation of the known acetal resins may produce significantdifferences in the structure of the obtained resin and thus insignificant differences of their properties. For example, incompletedissolution of the poly(vinyl alcohol) reagent may lead to anirreproducible degree of conversion, i.e. a lack of control of thecomposition of the final product. Also the competition and thetransacetylisation which often occurs between the mixed aldehydereagents is difficult to control so that the right balance between thehydrophobicity of the resin and its solubility in an alkaline developercannot always be obtained.

In the unpublished patent application PCT/EP2013/075366 filed on Jan. 12013, (ethylene, vinyl acetal) copolymers and their use in lithographicprinting plate precursors are disclosed.

With the so-called thermal digital plates, an infrared laser is used toimage infrared radiation sensitive precursors. These infrared radiationsensitive precursors have as a common ingredient a compound thattriggers the imaging mechanism by absorbing and converting the infraredradiation, which is used to image the precursors, into heat. Suchcompounds are often dyes, commonly referred to as IR-dyes. It has beenobserved that such IR-dyes, present as major ingredients in the coatingof the precursors, can also have a negative impact on these precursors.For example, it has been observed that IR-dyes may be inhomogeneouslydistributed or even form aggregates in the coating of a printing platedue to their poor solubility in common coating solvents. Such aggregatesmay tend to form so-called hot spots in the coating leading to unwantedpartial ablation. The generation of ablation debris may contaminate theelectronics and optics of exposure devices. In addition, IR-dyes mayform crystals in the coating which may locally influence thesolubilisation behaviour of the coating. As a result, a poordifferentiation between image and non-image areas may be obtainedleading to a poor printing quality. The occurrence of thesecrystallization defects may become more pronounced when the printingplate precursor is stored before exposure and development, i.e. thestorage stability of the precursor is poor.

EP 1 297 950 discloses a heat-sensitive lithographic printing plateprecursor comprising a polymer which is soluble in an aqueous alkalinesolution and which comprises at least one chromophoric moiety having alight absorption maximum in the wavelength range between 400 and 780 nm.

U.S. Pat. No. 6,124,425 discloses a reactive infrared absorbing polymerhaving a molecular weight of more than 5000 which comprises a nearinfrared absorbing segment, a processing segment and a thermallyreactive segment.

WO 2001/94123 discloses a printing form precursor which includes on asubstrate a thermally imageable coating including a polymer comprising apendant infrared absorbing agent and a cover layer. Such precursorsavoid migration of the dyes and errors in manufacturing leading toinconsistent batches.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide poly(vinylacetal) resins which are suitable for lithographic platemaking and whichhave the known advantages of this class of polymers such as a highabrasion resistance but which are intrinsically less susceptible toprocess conditions during their preparation. These advantages andbenefits are realised by the (ethylene, vinyl acetal) copolymer definedbelow, of which the hydrophobicity is defined by ethylenic moieties inthe backbone of the polymer which can be controlled independently fromthe acetal moieties. In the coating of lithographic printing platesthese polymers provide an improved sensitivity and abrasion resistancecompared to poly(vinyl acetal) resins of the prior art while the balancebetween the ink acceptance, arising from the ethylenic moieties, and thesolubility in an alkaline developer, arising form the acetal moieties,can be controlled efficiently.

A preferred (ethylene, vinyl acetal) copolymer comprises (i) a pluralityof ethylenic moieties A having a structure according to the followingformula:

wherein R² and R³ independently represent hydrogen, a halogen or anoptionally substituted linear, branched or cyclic alk(en)yl group, or anoptionally substituted aromatic group or heteroaromatic group, and (ii)a plurality of acetal moieties B having a structure according to thefollowing formula:

whereinL¹ represents a divalent linking group;

X=0 or 1; and

R¹ represents an optionally substituted aromatic or heteroaromatic groupincluding at least one hydroxyl group; and and (iii) a plurality ofacetal moieties C and/or moieties D which include a structural moietycomprising a chromophoric group that has its main absorption in theinfrared region.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention. Specificembodiments of the invention are also defined below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The poly(vinyl acetal) resin is a copolymer comprising a plurality ofethylenic moieties A, a plurality of acetal moieties B and a pluralityof acetal moieties C and/or moieties D. The term “ethylenic moiety” isgenerally understood as the monomeric unit—i.e. the building blockmaking up the polymer—obtained after polymerisation of optionallysubstituted ethylene. The ethylenic moieties comprise —CH₂—CH₂— as wellas mono- and/or di-substituted derivatives thereof. The poly(vinylacetal) resin is further also referred to herein as the “(ethylene,vinyl acetal) copolymer”.

The (ethylene, vinyl acetal) copolymer may be a random or ablock-copolymer. In the latter embodiment, the copolymer may includealternating sequences of blocks consisting of the ethylenic moieties Aand blocks consisting of the acetal moieties B and blocks consisting ofthe acetal moieties C and/or moieties D. Such blocks may range fromsmall blocks, e.g. comprising less than 5 moieties—i.e. 1, 2, 3, 4 or 5moieties—up to blocks comprising 100 moieties or more. Preferably, theblocks including the ethylenic moieties A, the blocks including theacetal moieties B and the blocks including the acetal moieties C and/ormoieties D independently include about 10 to 90, 15 to 80 or 20 to 60ethylenic moieties. The moieties A may be all the same or different.Likewise, the moieties B, C and/or D may be all the same or different.

The acetal moieties B have a structure according to the followingformula:

whereinL¹ represents a divalent linking group;

X=0 or 1; and

R¹ represents an aromatic or heteroaromatic group including at least onehydroxyl group and optionally one or more additional substituent(s). Thehydroxyl group(s) may be in ortho, meta and/or para-position on thering.

Suitable examples of the aromatic group include a phenyl, benzyl, tolyl,ortho-meta- or para-xylyl group, naphtyl, anthracenyl, phenanthrenylgroup and/or combinations thereof, which may contain, besides the atleast one hydroxyl group, further optional substituents. Theheteroaromatic group is preferably selected from an optionallysubstituted furyl, pyridyl, pyrimidyl, pyrazoyl, thiofenyl group and/orcombinations thereof, all including at least one hydroxyl group.

In the definition of R¹, the optional substituents on the aromatic orheteroaromatic group may be selected from additional hydroxysubstituents, an alkyl group such as a methyl or ethyl group, an alkoxygroup such as a methoxy or an ethoxy group, an aryloxy group, athioalkyl group, a thioaryl group, —SH, an azo group such as an azoalkylor azoaryl group, a thioalkyl, amino, ethenyl, phenyl, alkyl, alkenyl,alkynyl, cycloalkyl, aryl, heteroaryl or heteroalicyclic group and/orcombinations thereof.

Preferably, R¹ is an optionally substituted phenol or naphthol groupsuch as an optionally substituted 2-, 3- or 4-hydroxyphenyl group, a2,3-, 2,4-, 2,5-dihydroxyphenyl, a 1,2,3-trihydroxyphenyl or ahydroxynaphthyl group. More preferably, R¹ is an optionally substitutedphenol group. The optional substitutents are preferably an alkoxy groupsuch as a methoxy or an ethoxy group.

The divalent linking group L¹ is preferably selected from an optionallysubstituted alkylene, arylene or heteroarylene, —O—, —CO—, —CO—O—,—O—CO—, —CO—NH—, —NH—CO—, —NH—CO—O—, —O—CO—NH—, —NH—CO—NH—, —NH—CS—NH—,—SO—, —SO₂—, —CH═N—, —NH—NH— and/or combinations thereof. Thesubstituents optionally present on the alkylene, the arylene or theheteroarylene group may be represented by an alkyl group, a hydroxylgroup, an amino group, a (di)alkylamino group, an alkoxy group, aphosphonic acid group or a salt thereof. More preferably, the divalentlinking group L¹ represents an optionally substituted alkylene, aryleneor heteroarylene. Most preferably, L¹ represents —CH₂—, —CH₂—CH₂—,—CH₂—CH₂—CH₂— or a phenylene group.

In a highly preferred embodiment, the acetal moieties B have a structureaccording to the following formula:

wherein R¹ is as defined above.

The ethylenic moieties A have a structure according to the followingformula:

wherein R² and R³ independently represent hydrogen, a halogen such aschloro, bromo or iodo group, or an optionally substituted linear,branched or cyclic alk(en)yl group—i.e. an alkyl or alkenyl group—or anoptionally substituted aromatic group or an optionally substitutedheteroaromatic group. Examples of the alkyl group are a methyl, ethyl,n-propyl, n-butyl, n-pentyl, n-hexyl, chloromethyl, trichloromethyl,iso-propyl, iso-butyl, iso-pentyl, neo-pentyl, 1-methylbutyl andiso-hexyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl andmethylcyclohexyl group. Examples of the alkenyl group are ethenyl,n-propenyl, n-butenyl, n-pentenyl, n-hexenyl, iso-propenyl, iso-butenyl,iso-pentenyl, neo-pentenyl, 1-methylbutenyl, iso-hexenyl, cyclopentenyl,cyclohexenyl and methylcyclohexenyl group. The halogen is preferably achloro group. The aromatic group is preferably selected from anoptionally substituted aryl group such as a phenyl, benzyl, tolyl or anortho-meta- or para-xylyl group, an optionally substituted naphtyl,anthracenyl, phenanthrenyl, and/or combinations thereof. Theheteroaromatic group is preferably selected from an optionallysubstituted furyl, pyridyl, pyrimidyl, pyrazoyl or thiofenyl groupand/or combinations thereof. Preferably, R² and R³ independentlyrepresent hydrogen, a chloro group or a methyl group. In a mostpreferred embodiment, R² and R³ represent hydrogen.

The optional substituents on the linear, branched or cyclic alk(en)ylgroup and on the aromatic or heteroaromatic group may be selected froman alkoxy group such as a methoxy or an ethoxy group, a thioalkyl group,—SH, and/or a combinations thereof. The optional substituents on thearomatic or heteroaromatic group may further be selected from an aryloxygroup, a thioaryl group, an azo group such as an azoalkyl or azoarylgroup, an amino group and/or a combinations thereof.

In a highly preferred embodiment, the ethylenic moieties A have astructure according to the following formula:

wherein R² is as defined above.

The (ethylene, vinyl acetal) copolymer comprises besides the moieties Aand B as defined above, the acetal moieties C and/or moieties D whichinclude a structural moiety comprising a chromophoric group that has itsmain absorption in the infrared region.

Preferably the acetal moieties C and the moieties D have a structureaccording to the following formulae:

whereinL² and L³ represent a divalent linking group;y and z independently represent 0 or 1;R⁴ and R⁵ include a structural moiety comprising a chromophoric groupthat has its main absorption in the infrared region.

The linking groups L² and L³ independently represent a linking group asdefined above for the linking group L¹.

In a preferred embodiment of the present invention, the acetal moietiesC have a structure according to the following formula:

whereinR6 represents a structural moiety comprising a chromophoric group thathas its main absorption in the infrared region and the bond to thecenter of the aromatic ring means that any of the hydrogen atoms of thearomatic ring can be substituted by —O—R6: —OR6 may be in ortho, meta orpara position on the ring structure.

The chromophoric group has its main absorption in the infrared region,i.e. radiation having a wavelength in the range from 750 to 1500 nm,preferably in the range from 750 nm to 1250 nm, more preferably in therange from 750 nm to 1100 nm, and most preferably in the range from 780nm to 900 nm. Preferably the chromophoric group has its absorptionmaximum in the infrared region. Preferably, the term “chromophoricmoiety” corresponds to a group including a conjugated system.

Useful chromophoric groups correspond to the dyes given in The Chemistryand Application of Dyes, edited by D. R. Waring and G. Hallas (PlenumPress New York and London, 1990). Suitable dye classes can be selectedfrom the group consisting of indoaniline dyes, azomethine dyes, azodyes, di- and triaryl carbonium dyes and their heteroatomiccounterparts, anthraquinone dyes, benzodifuranone dyes, polycyclicaromatic carbonyl dyes, indigoid dyes, cyanines, oxonoles, hemicyanines,azacarbocyanines, merocyanines, hemicyanines, carbostyryl dyes,phthalocyanines, quinophtalones, nitro and nitroso dyes, formazan dyesand stylbene dyes. The dyes can also be complexes of transition metals,typically e.g. copper or iron complexes. Most preferably, thechromophoric moiety is derived from cyanine dyes, indoaniline dyes,azomethine dyes, azo dyes or anthraquinone dyes.

The chromophoric group preferably has a structure according to GeneralFormula I:

whereinT and T′ independently represent one or more substituents or anannulated ring;Z and Z′ independently represent —O—, —S—, —CR^(e)R^(f)— or —CH═CH— andwherein R^(e) and R^(f) independently represent an optionallysubstituted alkyl or aryl group;R^(z) and R^(z′) independently represent an optionally substituted alkylgroup;R^(b) and R^(c) independently represent a hydrogen atom or an optionallysubstituted alkyl group or represent the necessary atoms to form anoptionally substituted ring structure;R^(a) and R^(d) independently represent a hydrogen atom or an optionallysubstituted alkyl group;R^(z) and R^(a) or R^(d) and R^(z′) may represent the necessary atoms toform an optionally substituted 5- or 6-membered ring;X⁻ renders the chromophoric group neutral; and* denotes the linking position.

In a preferred embodiment, Z and Z′ represent —CR^(e)R^(f)— whereinR^(e) and R^(f) represent an alkyl group, preferably a methyl group;R^(a) and R^(d) represent a hydrogen atom; and R^(b) and R^(c) representthe necessary atoms to form an optionally substituted ring structure;preferably a five or six membered carbocyclic or aromatic ring, mostpreferably a six membered carbocyclic ring.

Preferably X⁻ represents a halide anion, i.e. Cl⁻, Br⁻ or I⁻; asulfonate group anion, e.g. CH₃SO₃ ⁻, CF₃SO₃ ⁻, p-toluene sulfonate; atetrafluoroborate or a hexafluorophosphate anion. Most preferably, X⁻represents p-toluene sulfonate.

The one or more substituents T and T′ may be independently selected fromhalogen such as a chloro, bromo or iodo atom, an optionally substitutedalkyl group, an optionally substituted (hetero)alkyl group, an alkoxygroup, a cyano group, —CO₂R^(t), —CF₃ and —SO₂R^(t′) and wherein R^(t)represents a hydrogen atom or an optionally substituted alkyl group andR^(t′) represents an optionally substituted alkyl or an optionallysubstituted (hetero)aryl group.

The chromophoric group according to general formula I is preferablycationic meaning that none of the substituents contain an anionic group.

In a preferred embodiment, the weight ratio of the weight of thechromophoric group in the polymer to the total weight of the polymer isless than 25 wt %, preferably less than 15% wt, more preferably lessthen 10 wt % and most preferably between 2 and 7.5 wt %.

The acetal moiety C is preferably prepared by post-modification of anacetal moiety bearing at least one hydroxy substituted group.Preferably, the acetal moiety C is prepared by acylation, acetalysationor alkylation of such an acetal precursor moiety—i.e. an acetal moietybearing at least one hydroxy substituted group. An alkylation reactionof such an acetale precursor moiety is particularly preferred. Forexample, the acetal moiety C can be prepared by reacting a chromophoricgroup according to General Formula II including a leaving group in themeso-position, preferably a chloride leaving group, with a hydroxy groupon the acetal precursor moiety.

wherein Y represents a leaving group and all the other substituents areas defined in General Formula I.

The leaving group Y preferably represents a halogen such as a fluorine,chlorine, bromine or iodine, more preferably chlorine or iodine and mostpreferably a chlorine.

Typical examples of resins including acetal moieties bearing hydroxysubstituted groups suitably used for the preparation of acetal moietiesC, are given below without being limited thereto. The polymers arerepresented by their main structural elements, independent from themonomer ratios.

Typical examples of chromophoric groups according to General Formula IIincluding a leaving group in the meso-position, suitably used asprecursors in the preparation of the resins according to the presentinvention are given in the Table below without being limited thereto.

Preferably the (ethylene, vinyl acetal) copolymer comprises ethylenicmoieties A as defined above in an amount of at least 10 mol %,preferably in a range from 10 to 55 mol %, more preferably in a rangefrom 15 to 45 mol %, and most preferably in a range from 20 to 35 mol %.The acetal moieties B as defined above are preferably present in anamount of at least 15 mol %, preferably in a range from 15 to 60 mol %,more preferably in a range from 20 to 50 mol %, and most preferably in arange from 25 to 45 mol %. The acetal moieties C as defined above, ifpresent, are preferably present in an amount of at least 0.25 mol %,preferably in a range from 0.25 to 25 mol %, more preferably in a rangefrom 0.5 to 20 mol %, and most preferably in a range from 1 to 15 mol %.The acetal moieties D as defined above are, if present, preferablypresent in an amount of at least 0.25 mol %, preferably in a range from0.25 to 25 mol %, more preferably in a range from 0.5 to 20 mol %, andmost preferably in a range from 1 to 15 mol %. All amounts of themoieties, expressed herein as mol %, refer to the sum of all monomericunits of the copolymer.

In a preferred embodiment, the sum of the amounts of all the moieties A,and of all the moieties B and of all the moieties C and/or moieties D inthe copolymer ranges from 50 to 90 mol %, more preferably from 60 to 80mol %, and most preferably from 65 to 75 mol %. Preferably, the(ethylene, vinyl acetal) copolymer comprises the moieties A, B and C.

The (ethylene, vinyl acetal) copolymer may comprise other monomericunits besides moieties A, B, C and D as defined above. The copolymer mayfor example further comprise optionally substituted vinyl alcohol,referred to herein as moieties E, and/or moieties F represented by thefollowing formula:

wherein R⁷ represents hydrogen, or an optionally substituted linear,branched or cyclic alkyl group such as a methyl, ethyl, n-propyl,n-butyl, n-pentyl, n-hexyl, chloromethyl, trichloromethyl, iso-propyl,iso-butyl, iso-pentyl, neo-pentyl, 1-methylbutyl and iso-hexylcyclopropyl, cyclobutyl, cyclopentyl, methyl cyclohexyl, cyclohexylgroup, an optionally substituted aromatic group or an optionallysubstituted heteroaromatic group. In a preferred embodiment, R⁷ is anoptionally substituted alkyl group, most preferably methyl.

In the above definition of R⁷, the optional substituents on the linear,branched or cyclic alkyl group and the aromatic or heteroaromatic groupmay be selected from an alkoxy group such as a methoxy or an ethoxygroup, a thioalkyl group, —SH, and/or a combinations thereof. Theoptional substituents on the aromatic or heteroaromatic group mayfurther be selected from an aryloxy group, a thioaryl group, an azogroup such as an azoalkyl or azoaryl group, an amino group, and/or acombinations thereof.

The amount of vinyl alcohol moieties E is preferably from 10 to 60 mol%, more preferably from 15 to 50 mol %, and most preferably from 20 to30 mol %. The amount of moieties F is preferably between 0 and 10 mol %.Preferably the amount of moieties F is less than 8 mol %, morepreferably less than 3 mol % and most preferably less than 1 mol %.

In a preferred embodiment of the present invention, the (ethylene, vinylacetal) copolymer is represented by the general formula:

wherein R¹, R⁴, y and L² are as defined above and R⁷ is an optionallysubstituted alkyl group, preferably methyl;m=10 to 55 mol %, more preferably 15 to 45 mol %, and most preferably 20to 35 mol %;n=15 to 60 mol %, more preferably 20 to 50 mol %, and most preferably 25to 45 mol %;o=10 to 60 mol %, more preferably 15 to 50 mol %, and most preferably 20to 30 mol %; andp=0 to 10 mol %, more preferably less than 3 mol % and most preferablyless than 1 mol %;q=0.25 to 25 mol %, more preferably 0.5 to 20 mol %, and most preferably1 to 15 mol %.

The numeric average molecular weight (Mn) of the copolymers rangespreferably from 15000 to 250000, more preferably from 25000 to 200000and most preferably from 35000 to 150000. The weight average molecularweight (Mw) of the copolymers ranges preferably from 50000 to 350000,more preferably from 70000 to 325000 and most preferably from 100000 to300000. The numeric average molecular weight (Mn) and the weight averagemolecular weight (Mw) are each determined by size exclusionchromatography.

The copolymer can, besides moieties A, B, C, D, E and F discussed above,contain further monomeric units as disclosed in U.S. Pat. No. 5,169,897,WO 1993/3068, U.S. Pat. No. 5,534,381, U.S. Pat. No. 5,698,360, JP11-212252, JP 11-231535, JP 2000-039707, JP 2000-275821, JP 2000-275823,U.S. Pat. No. 6,087,066, WO 2001/9682, U.S. Pat. No. 6,270,938, U.S.Pat. No. 6,596,460, WO 2002/73315, WO 2002/96961, U.S. Pat. No.6,818,378, WO 2004/20484, WO 2007/3030, WO 2009/5582 or WO 2009/99518.

The copolymers described herein can be prepared using known reagentiaand reaction conditions including those described in U.S. Pat. No.6,541,181, U.S. Pat. No. 4,665,124, U.S. Pat. No. 4,940,646, U.S. Pat.No. 5,169,898, U.S. Pat. No. 5,700,619, U.S. Pat. No. 5,792,823, U.S.Pat. No. 5,849,842, WO 93/03068, DE 10011096; DE 3404366, U.S. Ser. No.09/751,660, WO 01/09682, WO 03/079113, WO 2004/081662, WO 2004/020484,WO 2008/103258, and in JP 09-328,519.

Suitable polymers which can be used as starting material are copolymersof optionally substituted ethylene and vinyl alcohol. Acetalisation oftwo neighbouring vinyl alcohol units thereof with an aldehyde producesacetal moieties B.

Examples of such aldehydes are e.g. phenolic aldehydes such aso-hydroxybenzaldehyde, 4,6-dibromo-2-formylphenol,3,5-dichlorosalicylaldehyde, 2,4-dihydroxybenzaldehyde,3-methoxysalicyladehyde, 6-hydroxysalicylaldehyde, phloroglucinaldehyde,m-hydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde,4-ethoxy-3-hydroxy-benzaldehyde, p-hydroxybenzaldehyde, syringaldehyde,4-hydroxy-3,5-di-tert-butylbenzaldehyde, 6-hydroxy-isophthalaldehydicacid and 1-hydroxy-2-anthraquinonecarboxaldehyde; naphthol aldehydessuch as 2-hydroxy-1-naphthalenealdehyde,4-hydroxy-1-naphthalenecarbaldehyde, 1-hydroxy-2-naphthaldehyde,6-hydroxy-2-naphthaldehyde and1,6,7-trihydroxy-2-naphthalenecarboxaldehyde; or antracenol aldehydessuch as 1,3-dihydroxy-2-anthracenecarboxaldehyde and2-hydroxy-1-anthracenecarboxaldehyde.

This acetalization reaction generally requires addition of a stronginorganic or organic catalyst acid. Examples of catalyst acids arehydrochloric acid, sulfuric acid, phosphoric acid, p-toluenesulfonicacid, alkylsulfonic acid, perfluoroalkylsulfonic acid and otherperfluoro-activated acids. The amount of acid added to the reactionmixture should allow effective protonation of the reagents but shouldnot significantly alter the final product by causing unwanted hydrolysisof the acetal groups. The applied reaction temperature is preferablybetween 0° C. and the boiling point of the solvent and depends on thekind of reagents and on the desired level of substitution. The reactionproduct obtained often remains in solution even if the initialpoly(ethylene, vinyl alcohol) reagent is not completely dissolved.Organic solvents as well as mixtures of water with organic solvents areused for the reaction. Incomplete dissolution of the poly(ethylene,vinyl alcohol) reagent is a disadvantage that may lead to anirreproducible degree of conversion. Therefore, in order to obtainreproducible products, solvents which allow complete dissolution of theinitial poly(ethylene, vinyl alcohol) reagent in the reaction mixtureare preferred. Suitable organic solvents are alcohols (such as methanol,ethanol, propanol, butanol, and glycol ether), cyclic ethers (such as1,4-dioxane), and dipolar aprotic solvents (such asN,N-dimethylformamid, N-methyl pyrrolidone or dimethyl sulfoxide). Thefinished products may be isolated as a solid, by introducing thereaction mixture into a non-solvent under vigorous stirring, followed byfiltering and drying. Water is especially suitable as a non-solvent forthe polymers. Unwanted hydrolysis of the acetal group containing ahydroxyl-substituted aromatic group takes place much easier than for theacetal groups containing an aliphatic or non-substituted aromatic group.The presence of small amounts of water in the reaction mixture may leadto a decreased degree of acetalization and incomplete conversion of thearomatic hydroxy aldehyde used. In the absence of water, thehydroxy-substituted aromatic aldehydes react with hydroxyl groups ofalcohols immediately and with almost 100% conversion. Therefore, it isdesirable to remove the water from the reaction mixture during thereaction by for example distillation under reduced pressure. Inaddition, the remaining water may be removed by adding organic compoundsto the reaction mixture which form volatile materials and/or inertcompounds upon reaction with water. These organic compounds may bechosen from e.g. carbonates, orthoesters of carbonic or carboxylic acidssuch as diethylcarbonate, trimethyl orthoformate, tetraethyl carbonate,and tetraethyl silicate such as silica-containing compounds. Theaddition of these materials to the reaction mixture typically leads to100% conversion of the used aldehydes.

Specific examples of copolymers according to the present invention aregiven in the following Table:

The (ethylene, vinyl acetal) copolymer can be used as a binder in thecoating of an image recording material such as a lithographic printingplate precursor or a printed circuit board precursor. The lithographicprinting plate precursor preferably includes a heat and/or lightsensitive coating and is preferably positive-working, i.e. afterexposure and development the exposed areas of the coating are removedfrom the support and define hydrophilic (non-printing) areas, whereasthe unexposed coating is not removed from the support and definesoleophilic (printing) areas.

The light and/or heat-sensitive coating which includes the (ethylene,vinyl acetal) copolymer, may comprise one layer or more than one layer.Preferably, the coating comprises at least two layers; a first layer,and a second layer located above said first layer. First layer meansthat the layer is, compared to the second layer, located closer to thelithographic support. The poly(vinyl acetale) binder may be present inthe first layer, in the second layer or in the first and the secondlayer. The poly(vinyl acetal) binder is preferably only present in thesecond layer.

The light and/or heat sensitive coating preferably contains, besides the(ethylene, vinyl acetal) copolymer, an alkaline soluble oleophilicresin. The oleophilic resin present in the coating is preferably apolymer that is soluble in an aqueous developer, more preferably anaqueous alkaline developing solution with a pH between 7.5 and 14. Theoleophilic resin is preferably a phenolic resin selected from a novolac,a resol or a polyvinylphenolic resin. Other preferred polymers arephenolic resins wherein the phenyl group or the hydroxy group of thephenolic monomeric unit are chemically modified with an organicsubstituent as described in EP 894 622, EP 901 902, EP 933 682,WO99/63407, EP 934 822, EP 1 072 432, U.S. Pat. No. 5,641,608, EP 982123, WO99/01795, WO04/035310, WO04/035686, WO04/035645, WO04/035687 orEP 1 506 858. One or more alkaline soluble oleophilic resins may bepresent in the first layer, in the second layer or in both the first andthe second layer. Preferably, one or more alkaline soluble oleophilicresin(s)—preferably a resole resin—is present in the layer including thepoly(vinyl acetal) binder. In the embodiment where the poly(vinylacetal) binder is only present in the first layer, one or more alkalinesoluble oleophilic resin(s)—preferably a novolac resin—is present in thesecond layer.

In the embodiment where the poly(vinyl acetal) binder is at leastpresent in the second layer, the amount of phenolic resin optionallypresent in the coating is preferably at least 10% by weight relative tothe total weight of all the components present in the coating.Preferably, the amount of phenolic resin optionally present in thecoating is between 10 and 40% by weight, more preferably between 12 and35% by weight, most preferably between 15 and 30% by weight.

In the embodiment where the poly(vinyl acetal) binder is only present inthe first layer, the amount of phenolic resin present in the coating ispreferably at least 20% by weight, more preferably at least 30% byweight and most preferably at least 45% by weight. Alternatively, theamount of phenolic resin in the latter embodiment is preferably between25 and 65% by weight, more preferably between 35 and 60% wt weight andmost preferably between 45 and 55% wt.

The novolac resin or resol resin may be prepared by polycondensation ofaromatic hydrocarbons such as phenol, o-cresol, p-cresol, m-cresol,2,5-xylenol, 3,5-xylenol, resorcinol, pyrogallol, bisphenol, bisphenolA, trisphenol, o-ethylphenol, p-etylphenol, propylphenol, n-butylphenol,t-butylphenol, 1-naphtol and 2-naphtol, with at least one aldehyde orketone selected from aldehydes such as formaldehyde, glyoxal,acetoaldehyde, propionaldehyde, benzaldehyde and furfural and ketonessuch as acetone, methyl ethyl ketone and methyl isobutyl ketone, in thepresence of an acid catalyst. Instead of formaldehyde and acetaldehyde,paraformaldehyde and paraldehyde may, respectively, be used. The weightaverage molecular weight, measured by gel permeation chromatographyusing universal calibration and polystyrene standards, of the novolacresin is preferably from 500 to 150,000 g/mol, more preferably from1,500 to 50,000 g/mol.

The poly(vinylphenol) resin may be a polymer of one or morehydroxy-phenyl containing monomers such as hydroxystyrenes orhydroxy-phenyl (meth)acrylates. Examples of such hydroxystyrenes areo-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene,2-(o-hydroxyphenyl)propylene, 2-(m-hydroxyphenyl)propylene and2-(p-hydroxyphenyl)propylene. Such a hydroxystyrene may have asubstituent such as chloro, bromo, iodo or fluoro group or a C₁₋₄ alkylgroup, on its aromatic ring. An example of such hydroxy-phenyl(meth)acrylate is 2-hydroxy-phenyl methacrylate. The poly(vinylphenol)resin may be prepared by polymerizing one or more hydroxy-phenylcontaining monomer in the presence of a radical initiator or a cationicpolymerization initiator, or by copolymerizing of one or more of thesehydroxy-phenyl containing monomers with other monomeric compounds suchas acrylate monomers, methacrylate monomers, acrylamide monomers,methacrylamide monomers, vinyl monomers, aromatic vinyl monomers ordiene monomers. The weight average molecular weight, measured by gelpermeation chromatography using universal calibration and polystyrenestandards, of the poly(vinylphenol) resin is preferably from 1,000 to200,000 g/mol, more preferably from 1,500 to 50,000 g/mol.

The heat-sensitive coating may further contain one or more otherbinder(s) which is insoluble in water and soluble in an alkalinesolution such as an organic polymer which has acidic groups with a pKaof less than 13 to ensure that the layer is soluble or at leastswellable in aqueous alkaline developers. This additional binder may bepresent in the first layer, in the second layer or in both the first andthe second layer. Preferably, the binder is present in the first layerlocated between the second layer including the poly(vinyl acetal) binderand the hydrophilic support. The binder may be selected from a polyesterresin, a polyamide resin, an epoxy resin, an acrylic resin, amethacrylic resin, a styrene based resin, a polyurethane resin or apolyurea resin. The binder may have one or more functional groups. Thefunctional group(s) can be selected from the list of

-   -   (i) a sulfonamide group such as —NR—SO₂—, —SO₂—NR— or —SO₂—NR′R″        wherein R and R′ independently represent hydrogen or an        optionally substituted hydrocarbon group such as an optionally        substituted alkyl, aryl or heteroaryl group; more details        concerning these polymers can be found in EP 2 159 049;    -   (ii) a sulfonamide group including an acid hydrogen atom such as        —SO₂—NH—CO— or —SO₂—NH—SO₂— as for example disclosed in U.S.        Pat. No. 6,573,022; suitable examples of these compounds include        for example N-(p-toluenesulfonyl) methacrylamide and        N-(p-toluenesulfonyl) acrylamide;    -   (iii) an urea group such as —NH—CO—NH—, more details concerning        these polymers can be found in WO 01/96119;    -   (iv) a star polymer in which at least three polymer chains are        bonded to a core as described in EP 2 497 639;    -   (v) a carboxylic acid group;    -   (vi) a nitrile group;    -   (vii) a sulfonic acid group; and/or    -   (viii) a phosphoric acid group.

(Co)polymers including a sulfonamide group are preferred. Sulfonamide(co)polymers are preferably high molecular weight compounds prepared byhomopolymerization of monomers containing at least one sulfonamide groupor by copolymerization of such monomers and other polymerizablemonomers. Preferably, in the embodiment where the poly(vinyl acetal)binder is present in the second layer, the copolymer comprising at leastone sulfonamide group is present in the first layer located between thelayer including the poly(vinyl acetal) binder and the hydrophilicsupport.

Examples of monomers copolymerized with the monomers containing at leastone sulfonamide group include monomers as disclosed in EP 1 262 318, EP1 275 498, EP 909 657, EP 1 120 246, EP 894 622, U.S. Pat. No.5,141,838, EP 1 545 878 and EP 1 400 351. Monomers such as alkyl or aryl(meth)acrylate such as methyl (meth)acrylate, ethyl (meth)acrylate,butyl (meth)acrylate, benzyl (meth)acrylate, 2-phenylethyl(meth)acrylate, hydroxylethyl (meth) acrylate, phenyl (meth) acrylate;(meth)acrylic acid; (meth)acrylamide; a N-alkyl or N-aryl(meth)acrylamide such as N-methyl (meth)acrylamide, N-ethyl(meth)acrylamide, N-phenyl (meth)acrylamide, N-benzyl (meth)acrylamide,N-methylol (meth)acrylamide, N-(4-hydroxyphenyl)(meth)acrylamide,N-(4-methylpyridyl)(meth)acrylate; (meth)acrylonitrile; styrene; asubstituted styrene such as 2-, 3- or 4-hydroxy-styrene, 4-benzoicacid-styrene; a vinylpyridine such as 2-vinylpyridine, 3-vinylpyridine,4-vinylpyridine; a substituted vinylpyridine such as4-methyl-2-vinylpyridine; vinyl acetate, optionally the copolymerisedvinyl acetate monomeric units are at least partially hydrolysed, formingan alcohol group, and/or at least partially reacted by an aldehydecompound such as formaldehyde or butyraldehyde, forming an acetal orbutyral group; vinyl alcohol; vinyl acetal; vinyl butyral; a vinyl ethersuch as methyl vinyl ether; vinyl amide; a N-alkyl vinyl amide such asN-methyl vinyl amide, caprolactame, vinyl pyrrolydone; maleimide; aN-alkyl or N-aryl maleimide such as N-benzyl maleimide, are preferred.

Suitable examples of sulfonamide (co)polymers and/or their method ofpreparation are disclosed in EP 933 682, EP 982 123, EP 1 072 432, WO99/63407, EP 1 400 351 and EP 2 159 049. A highly preferred example of asulfonamide (co)polymer is described in EP 2 047 988 A in [0044] to[0046].

Specific preferred examples of sulphonamide (co)polymers are polymerscomprising N-(p-aminosulfonylphenyl) (meth)acrylamide,N-(m-aminosulfonylphenyl) (meth)acrylamide N-(o-aminosulfonylphenyl)(meth)acrylamide and or m-aminosulfonylphenyl (meth) acrylate.

(Co)polymers including an imide group are also preferred as a binder inthe heat-sensitive coating. Specific examples include derivatives ofmethyl vinyl ether/maleic anhydride copolymers and derivatives ofstyrene/maleic anhydride copolymers, that contain an N-substitutedcyclic imide monomeric units and/or N-substituted maleimides such as aN-phenylmaleimide monomeric unit and a N-benzyl-maleimide monomericunit. Preferably, this copolymer is present in the first layer locatedbetween the layer including the poly(vinyl acetal) binder and thehydrophilic support. This copolymer is preferably alkali soluble.Suitable examples are described in EP 933 682, EP 894 622 A [0010] to[0033], EP 901 902, EP 0 982 123 A [007] to [0114], EP 1 072 432 A[0024] to [0043] and WO 99/63407 (page 4 line 13 to page 9 line 37).

Polycondensates and polymers having free phenolic hydroxyl groups, asobtained, for example, by reacting phenol, resorcinol, a cresol, axylenol or a trimethylphenol with aldehydes, especially formaldehyde, orketones, may also be added to the heat-sensitive coating. Condensates ofsulfamoyl- or carbamoyl-substituted aromatics and aldehydes or ketonesare also suitable. Polymers of bismethylol-substituted ureas, vinylethers, vinyl alcohols, vinyl acetals or vinylamides and polymers ofphenylacrylates and copolymers of hydroxyphenylmaleimides are likewisesuitable. Furthermore, polymers having units of vinylaromatics or aryl(meth)acrylates may be mentioned, it being possible for each of theseunits also to have one or more carboxyl groups, phenolic hydroxylgroups, sulfamoyl groups or carbamoyl groups. Specific examples includepolymers having units of 2-hydroxyphenyl (meth)acrylate, of4-hydroxystyrene or of hydroxyphenylmaleimide. The polymers mayadditionally contain units of other monomers which have no acidic units.Such units include vinylaromatics, methyl (meth)acrylate,phenyl(meth)acrylate, benzyl (meth)acrylate, methacrylamide oracrylonitrile.

The dissolution behavior of the coating can be fine-tuned by optionalsolubility regulating components. More particularly, developabilityenhancing compounds, development accelerators and development inhibitorscan be used. In the embodiment where the coating comprises more than onelayer, these ingredients can be added to the first layer and/or to thesecond layer and/or to an optional other layer of the coating.

Suitable developability enhancing compounds are (i) compounds which uponheating release gas as disclosed in WO 2003/79113, (ii) the compounds asdisclosed in WO 2004/81662, (iii) the compositions that comprises one ormore basic nitrogen-containing organic compounds as disclosed in WO2008/103258 and (iv) the organic compounds having at least one aminogroup and at least one carboxylic acid group as disclosed in WO2009/85093.

Examples of basic nitrogen-containing organic compounds useful in thedevelopability-enhancing compositions areN-(2-hydroxyethyl)-2-pyrrolidone, 1-(2-hydroxyethyl)piperazine,N-phenyldiethanolamine, triethanolamine,2-[bis(2-hydroxyethyl)amino]-2-hydroxymethyl-1.3-propanediol,N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine,N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine,3-[(2-hydroxyethyl)phenylamino]propionitrile, andhexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine. PreferablyN,N,N′,N′-tetrakis(2-hydroxypropyl)-ethylenediamine is used. Mixtures oftwo or more of these compounds are also useful. The basicnitrogen-containing organic compounds can be obtained from a number ofcommercial sources including BASF (Germany) and Aldrich Chemical Company(Milwaukee, Wis.).

The basic nitrogen-containing organic compound(s) is preferably presentin the coating in an amount of from 1 to 30% wt, and typically from 3 to15% wt, based on the total solids of the coating composition.

Preferably, one or more of the basic nitrogen-containing organiccompounds are used in combination with one or more acidicdevelopability-enhancing compounds, such as carboxylic acids or cyclicacid anhydrides, sulfonic acids, sulfinic acids, alkylsulfuric acids,phosphonic acids, phosphinic acids, phosphonic acid esters, phenols,sulfonamides, or sulfonimides, since such a combination may permitfurther improved developing latitude and printing durability.Representative examples of the acidic developability-enhancing compoundsare provided in [0030] to [0036] of US 2005/0214677. They may be presentin an amount of from 0.1 to 30% wt based on the total dry weight of thecoating composition. The molar ratio of one or more basicnitrogen-containing organic compounds to one or more acidicdevelopability-enhancing compounds is generally from 0.1:1 to 10:1 andmore typically from 0.5:1 to 2:1.

Polymeric developability enhancing compounds combined with a lowmolecular weight developability enhancing compound as described aboveare also of interest. The polymeric compound preferably has a molecularweight above 1500 g/mol and is present in an amount preferably less than40% wt of the total coating composition, more preferably less than 10%wt and most preferably less than 5% wt. The low molecular weightcomponent preferably has a molecular weight below 1500 g/mol and ispresent in an amount preferably less than 10% wt of the total weightcomposition, more preferably less than 5% wt and most preferably lessthan 2.5% wt. This type of contrast-enhancing system is preferably usedin low pH developers, pH<12, which are substantially free of silicates.

The polymeric compound may be a derivative of a glycol such as forexample polyethylenoxide, polypropyleneoxide and/or copolymers thereof,or a phenolic resin having a molecular weight lower than 100000 g/mol.

Specific examples of such high and low molecular weight developabilityenhancing compounds which are suitably used together are for examplehyperbranched polyesters such as the Boltorn™ products commerciallyavailable from Perstorp, and the following compounds:

Development accelerators are compounds which act as dissolutionpromoters because they are capable of increasing the dissolution rate ofthe coating. For example, cyclic acid anhydrides, phenols or organicacids can be used in order to improve the aqueous developability.Examples of the cyclic acid anhydride include phthalic anhydride,tetrahydrophthalic anhydride, hexahydrophthalic anhydride,3,6-endoxy-4-tetrahydrophthalic anhydride, tetrachlorophthalicanhydride, maleic anhydride, chloromaleic anhydride, alpha-phenylmaleicanhydride, succinic anhydride, and pyromellitic anhydride, as describedin U.S. Pat. No. 4,115,128. Examples of the phenols include bisphenol A,p-nitrophenol, p-ethoxyphenol, 2,4,4′-trihydroxybenzophenone,2,3,4-trihydroxy-benzophenone, 4-hydroxybenzophenone,4,4′,4″-trihydroxy-triphenylmethane, and4,4′,3″,4″-tetrahydroxy-3,5,3′,5′-tetramethyltriphenyl-methane, and thelike. Examples of the organic acids include sulphonic acids, sulfinicacids, alkylsulfuric acids, phosphonic acids, phosphates, and carboxylicacids, as described in, for example, JP-A Nos. 60-88,942 and 2-96,755.Specific examples of these organic acids include p-toluenesulphonicacid, dodecylbenzenesulphonic acid, p-toluenesulfinic acid,ethylsulfuric acid, phenylphosphonic acid, phenylphosphinic acid, phenylphosphate, diphenyl phosphate, benzoic acid, isophthalic acid, adipicacid, p-toluic acid, 3,4-dimethoxybenzoic acid, 3,4,5-trimethoxybenzoicacid, 3,4,5-trimethoxycinnamic acid, phthalic acid, terephthalic acid,4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid,n-undecanoic acid, and ascorbic acid. The amount of the cyclic acidanhydride, phenol, or organic acid contained in the coating ispreferably in the range of 0.05 to 20% by weight, relative to thecoating as a whole. Polymeric development accelerators such asphenolic-formaldehyde resins comprising at least 70 mol % meta-cresol asrecurring monomeric units are also suitable development accelerators.

In a preferred embodiment, the coating also contains developerresistance means, also called development inhibitors, i.e. one or moreingredients which are capable of delaying the dissolution of theunexposed areas during processing. The dissolution inhibiting effect ispreferably reversed by heating, so that the dissolution of the exposedareas is not substantially delayed and a large dissolution differentialbetween exposed and unexposed areas can thereby be obtained. Thecompounds described in e.g. EP 823 327 and WO 97/39894 act asdissolution inhibitors due to interaction, e.g. by hydrogen bridgeformation, with the alkali-soluble resin(s) in the coating. Inhibitorsof this type typically are organic compounds which include at least onearomatic group and a hydrogen bonding site such as a nitrogen atom whichmay be part of a heterocyclic ring or an amino substituent, an oniumgroup, a carbonyl, sulfinyl or sulfonyl group. Suitable dissolutioninhibitors of this type have been disclosed in e.g. EP 825 927 and EP823 327. Some of the compounds mentioned below, e.g. infrared dyes, suchas cyanines, and contrast dyes, such as quaternized triarylmethane dyes,can also act as a dissolution inhibitor.

Other suitable inhibitors improve the developer resistance because theydelay the penetration of the aqueous alkaline developer into thecoating. Such compounds can be present in the first layer and/or in theoptional second layer and/or in a development barrier layer on top ofsaid layer, as described in e.g. EP 864 420, EP 950 517, WO 99/21725 andWO 01/45958. The solubility and/or penetrability of the barrier layer inthe developer can be increased by exposure to heat and/or infraredlight.

Water-repellent polymers represent another type of suitable dissolutioninhibitors. Such polymers seem to increase the developer resistance ofthe coating by repelling the aqueous developer from the coating. Thewater-repellent polymers can be added to the first and/or second layerof the coating and/or can be present in a separate layer provided on topof these layers. In the latter embodiment, the water-repellent polymerforms a barrier layer which shields the coating from the developer andthe solubility of the barrier layer in the developer or thepenetrability of the barrier layer by the developer can be increased byexposure to heat or infrared light, as described in e.g. EP 864 420, EP950 517 and WO99/21725.

Preferred examples of inhibitors which delay the penetration of theaqueous alkaline developer into the coating include water-repellentpolymers including siloxane and/or perfluoroalkyl units. Thepolysiloxane may be a linear, cyclic or complex cross-linked polymer orcopolymer. The term polysiloxane compound shall include any compoundwhich contains more than one siloxane group —Si(R,R′)—O—, wherein R andR′ are optionally substituted alkyl or aryl groups. Preferred siloxanesare phenylalkylsiloxanes and dialkylsiloxanes. The number of siloxanegroups in the polymer is at least 2, preferably at least 10, morepreferably at least 20. It may be less than 100, preferably less than60.

The water-repellent polymer may be a block-copolymer or agraft-copolymer including a polar block such as a poly- oroligo(alkylene oxide) and a hydrophobic block such as a long chainhydrocarbon group, a polysiloxane and/or a perfluorinated hydrocarbongroup. A typical example of a perfluorinated surfactant is Megafac F-177available from Dainippon Ink & Chemicals, Inc. Other suitable copolymerscomprise about 15 to 25 siloxane units and 50 to 70 alkyleneoxidegroups. Preferred examples include copolymers comprisingphenylmethylsiloxane and/or dimethylsiloxane as well as ethylene oxideand/or propylene oxide, such as Tego Glide 410, Tego Wet 265, TegoProtect 5001 or Silikophen P50/X, all commercially available from TegoChemie, Essen, Germany.

A suitable amount of such a water-repellent polymer in the coating isbetween 0.5 and 25 mg/m², preferably between 0.5 and 15 mg/m² and mostpreferably between 0.5 and 10 mg/m². When the water-repellent polymer isalso ink-repelling, e.g. in the case of polysiloxanes, higher amountsthan 25 mg/m² can result in poor ink-acceptance of the non-exposedareas. An amount lower than 0.5 mg/m² on the other hand may lead to anunsatisfactory development resistance.

It is believed that during coating and drying, the water-repellentpolymer or copolymer acts as a surfactant and tends to position itself,due to its bifunctional structure, at the interface between the coatingand air and thereby forms a separate top layer, even when applied as aningredient of the coating solution. Simultaneously, such surfactantsalso act as spreading agents which improve the coating quality.Alternatively, the water-repellent polymer or copolymer can be appliedin a separate solution, coated on top of the coating including one oroptional more layers. In that embodiment, it may be advantageous to usea solvent in the separate solution that is not capable of dissolving theingredients present in the other layers so that a highly concentratedwater-repellent phase is obtained at the top of the coating.

Optionally, the coating of the heat-sensitive printing plate precursormay contain an infrared light absorbing dye or pigment which, in theembodiment where the coating comprises more than one layer, may bepresent in the first layer, and/or in the second layer, and/or in anoptional other layer. Preferred IR absorbing dyes are cyanine dyes,merocyanine dyes, indoaniline dyes, oxonol dyes, pyrilium dyes andsquarilium dyes. Examples of suitable IR dyes are described in e.g.EP-As 823327, 978376, 1029667, 1053868, 1093934; WO 97/39894 and00/29214. A preferred compound is the following cyanine dye:

wherein X⁻ is a suitable counter ion such as tosylate.

The concentration of the optional IR-dye in the coating is preferablybetween 0.25 and 15.0% wt, more preferably between 0.5 and 10.0% wt,most preferably between 1.0 and 7.5% wt relative to the coating as awhole.

The coating may further comprise one or more colorant(s) such as dyes orpigments which provide a visible color to the coating and which remainin the coating at the image areas which are not substantially removedduring the processing step. As a result, a visible image is formed whichenables inspection of the lithographic image on the developed printingplate. Such dyes are often called contrast dyes or indicator dyes.Preferably, the dye has a blue color and an absorption maximum in thewavelength range between 600 nm and 750 nm. Typical examples of suchcontrast dyes are the amino-substituted tri- or diarylmethane dyes, e.g.crystal violet, methyl violet, victoria pure blue, flexoblau 630,basonylblau 640, auramine and malachite green. Also the dyes which arediscussed in depth in EP-A 400,706 are suitable contrast dyes.

Dyes such as di- or tri-arylmethane dyes, cyanine dyes, styryl dyes andmerostyryl dyes, which, combined with specific additives, only slightlycolor the coating but which become intensively colored after exposure,as described in for example WO2006/005688 may also be used as colorants.

To protect the surface of the coating of the heat and/or light sensitiveprinting plate precursors, in particular from mechanical damage, aprotective layer may also optionally be applied. The protective layergenerally comprises at least one water-soluble binder, such as polyvinylalcohol, polyvinylpyrrolidone, partially hydrolyzed polyvinyl acetates,gelatin, carbohydrates or hydroxyethylcellulose, and can be produced inany known manner such as from an aqueous solution or dispersion whichmay, if required, contain small amounts—i.e. less than 5% by weightbased on the total weight of the coating solvents for the protectivelayer—of organic solvents. The thickness of the protective layer cansuitably be any amount, advantageously up to 5.0 μm, preferably from 0.1to 3.0 μm, particularly preferably from 0.15 to 1.0 μm.

Optionally, the coating may further contain additional ingredients suchas surfactants, especially perfluoro surfactants, inorganic fillers orpolymers particles such as matting agents and spacers. Examples ofinorganic fillers include silicon or titanium dioxide particles,zirconium oxide, kaolin clays and derivatives, silicium oxide basedparticles optionally coated and/or modified, alumina oxide, fumed silicaand cerium oxide. The particles can be in the micrometer range,typically between 1 μm and 10 μm. More preferable, the particles are inthe nanometer-range i.e. between 10 nm and 900 nm.

Any coating method can be used for applying one or more coatingsolutions to the hydrophilic surface of the support. The multi-layercoating can be applied by coating/drying each layer consecutively or bythe simultaneous coating of several coating solutions at once. In thedrying step, the volatile solvents are removed from the coating untilthe coating is self-supporting and dry to the touch. However it is notnecessary (and may not even be possible) to remove all the solvent inthe drying step. Indeed the residual solvent content may be regarded asan additional composition variable by means of which the composition maybe optimized. Drying is typically carried out by blowing hot air ontothe coating, typically at a temperature of at least 70° C., suitably80-150° C. and especially 90-140° C. Also infrared lamps can be used.The drying time may typically be 15-600 seconds.

Between coating and drying, or after the drying step, a heat treatmentand subsequent cooling may provide additional benefits, as described inWO99/21715, EP-A 1074386, EP-A 1074889, WO00/29214, and WO/04030923,WO/04030924, WO/04030925.

The lithographic printing plate precursor comprises a support which hasa hydrophilic surface or which is provided with a hydrophilic layer. Thesupport may be a sheet-like material such as a plate or it may be acylindrical element such as a sleeve which can be slid around a printcylinder of a printing press. Preferably, the support is a metal supportsuch as aluminum or stainless steel. The support can also be a laminatecomprising an aluminum foil and a plastic layer, e.g. polyester film.

A particularly preferred lithographic support is a grained and anodizedaluminum support. The aluminum support has usually a thickness of about0.1-0.6 mm. However, this thickness can be changed appropriatelydepending on the size of the printing plate used and/or the size of theplate-setters on which the printing plate precursors are exposed. Thealuminum is preferably grained by electrochemical graining, and anodizedby means of anodizing techniques employing phosphoric acid or asulphuric acid/phosphoric acid mixture. Methods of both graining andanodization of aluminum are well known in the art.

By graining (or roughening) the aluminum support, both the adhesion ofthe printing image and the wetting characteristics of the non-imageareas are improved. By varying the type and/or concentration of theelectrolyte and the applied voltage in the graining step, different typeof grains can be obtained. The surface roughness is often expressed asarithmetical mean center-line roughness Ra (ISO 4287/1 or DIN 4762) andmay vary between 0.05 and 1.5 μm. The aluminum substrate has preferablyan Ra value between 0.30 μm and 0.60 μm, more preferably between 0.35 μmand 0.55 μm and most preferably between 0.40 μm and 0.50 μm. The lowerlimit of the Ra value is preferably about 0.1 μm. More detailsconcerning the preferred Ra values of the surface of the grained andanodized aluminum support are described in EP 1 356 926.

By anodising the aluminum support, its abrasion resistance andhydrophilic nature are improved. The microstructure as well as thethickness of the Al₂O₃ layer are determined by the anodising step, theanodic weight (g/m² Al₂O₃ formed on the aluminum surface) varies between1 and 8 g/m². The anodic weight is preferably between 1.5 g/m² and 5.0g/m², more preferably 2.5 g/m² and 4.0 g/m² and most preferably 2.5 g/m²and 3.5 g/m².

The grained and anodized aluminum support may be subject to a so-calledpost-anodic treatment to improve the hydrophilic character of itssurface. For example, the aluminum support may be silicated by treatingits surface with a solution including one or more alkali metal silicatecompound(s)—such as for example a solution including an alkali metalphosphosilicate, orthosilicate, metasilicate, hydrosilicate,polysilicate or pyrosilicate—at elevated temperature, e.g. 95° C.Silicated supports are preferred in the embodiment were the printingplate precursors are developed with a silicate-free developer solution.Post anodic treatment Alternatively, a phosphate treatment may beapplied which involves treating the aluminum oxide surface with aphosphate solution that may further contain an inorganic fluoride.Further, the aluminum oxide surface may be rinsed with a citric acid orcitrate solution, gluconic acid, or tartaric acid. This treatment may becarried out at room temperature or may be carried out at a slightlyelevated temperature of about 30 to 50° C. A further interestingtreatment involves rinsing the aluminum oxide surface with a bicarbonatesolution. Still further, the aluminum oxide surface may be treated withpolyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphoricacid esters of polyvinyl alcohol, polyvinylsulphonic acid,polyvinylbenzenesulphonic acid, sulphuric acid esters of polyvinylalcohol, acetals of polyvinyl alcohols formed by reaction with asulphonated aliphatic aldehyde, polyacrylic acid or derivates such asGLASCOL E15™ commercially available from Ciba Speciality Chemicals. Oneor more of these post treatments may be carried out alone or incombination. More detailed descriptions of these treatments are given inGB-A 1 084 070, DE-A 4 423 140, DE-A 4 417 907, EP-A 659 909, EP-A 537633, DE-A 4 001 466, EP-A 292 801, EP-A 291 760 and U.S. Pat. No.4,458,005.

In a preferred embodiment, the support is first treated with an aqueoussolution including one or more silicate compound(s) as described abovefollowed by the treatment of the support with an aqueous solutionincluding a compound having a carboxylic acid group and/or a phosphonicacid group, or their salts. Particularly preferred silicate compoundsare sodium or potassium orthosilicate and sodium or potassiummetasilicate. Suitable examples of a compound with a carboxylic acidgroup and/or a phosphonic acid group and/or an ester or a salt thereofare polymers such as polyvinylphosphonic acid, polyvinylmethylphosphonicacid, phosphoric acid esters of polyvinyl alcohol, polyacrylic acid,polymethacrylic acid and a copolymer of acrylic acid and vinylphosphonicacid. A solution comprising polyvinylphosphonic acid orpoly(meth)acrylic acid is highly preferred.

The support can also be a flexible support, which may be provided with ahydrophilic layer, hereinafter called ‘base layer’. The flexible supportis e.g. paper, plastic film or aluminum. Preferred examples of plasticfilm are polyethylene terephthalate film, polyethylene naphthalate film,cellulose acetate film, polystyrene film, polycarbonate film, etc. Theplastic film support may be opaque or transparent.

The base layer is preferably a cross-linked hydrophilic layer obtainedfrom a hydrophilic binder cross-linked with a hardening agent such asformaldehyde, glyoxal, polyisocyanate or a hydrolyzedtetra-alkylorthosilicate. The latter is particularly preferred. Thethickness of the hydrophilic base layer may vary in the range of 0.2 to25 μm and is preferably 1 to 10 μm. More details of preferredembodiments of the base layer can be found in e.g. EP 1 025 992.

The heat-sensitive plate precursor can be image-wise exposed directlywith heat, e.g. by means of a thermal head, or indirectly by infraredlight, preferably near infrared light. The infrared light is preferablyconverted into heat by an IR light absorbing compound as discussedabove. The heat-sensitive lithographic printing plate precursor ispreferably not sensitive to visible light, i.e. no substantial effect onthe dissolution rate of the coating in the developer is induced byexposure to visible light. Most preferably, the coating is not sensitiveto ambient daylight, i.e. the wavelength range including near UV light(300-400 nm) and visible light (400-750 nm).

The printing plate precursor can be exposed to infrared light by meansof e.g. LEDs or a laser. Most preferably, the light used for theexposure is a laser emitting near infrared light having a wavelength inthe range from about 750 to about 1500 nm, more preferably 750 to 1100nm, such as a semiconductor laser diode, a Nd:YAG or a Nd:YLF laser. Therequired laser power depends on the sensitivity of the plate precursor,the pixel dwell time of the laser beam, which is determined by the spotdiameter (typical value of modern plate-setters at 1/e² of maximumintensity: 5-25 μm), the scan speed and the resolution of the exposureapparatus (i.e. the number of addressable pixels per unit of lineardistance, often expressed in dots per inch or dpi; typical value:1000-4000 dpi).

Two types of laser-exposure apparatuses are commonly used: internal(ITD) and external drum (XTD) platesetters. ITD plate-setters forthermal plates are typically characterized by a very high scan speed upto 500 m/sec and may require a laser power of several Watts. XTDplatesetters for thermal plates having a typical laser power from about200 mW to about 1 W operate at a lower scan speed, e.g. from 0.1 to 10m/sec. An XTD platesetter equipped with one or more laser diodesemitting in the wavelength range between 750 and 850 nm is an especiallypreferred embodiment.

The known platesetters can be used as an off-press exposure apparatus,which offers the benefit of reduced press down-time. XTD platesetterconfigurations can also be used for on-press exposure, offering thebenefit of immediate registration in a multi-color press. More technicaldetails of on-press exposure apparatuses are described in e.g. U.S. Pat.No. 5,174,205 and U.S. Pat. No. 5,163,368.

After exposure, the precursor is developed whereby the non-image areasof the coating are removed by immersion in a developer, preferably anaqueous alkaline developer, which may be combined with mechanicalrubbing, e.g. by a rotating brush. The developer preferably comprises analkaline agent which may be an inorganic alkaline agent such as analkali metal hydroxide, an organic alkaline agent such as an amine,and/or an alkaline silicate such as an alkali metal silicate or analkali metal metasilicate. Silicate-based developers which have a ratioof silicon dioxide to alkali metal oxide of at least 1 are advantageousbecause they ensure that the alumina layer (if present) of the substrateis not damaged. Preferred alkali metal oxides include Na₂O and K₂O, andmixtures thereof. A particularly preferred silicate-based developersolution is a developer solution comprising sodium or potassiummetasilicate, i.e. a silicate where the ratio of silicon dioxide toalkali metal oxide is 1. The developer preferably has a pH above 8, morepreferably above 10 and most preferably above 12. The developer mayfurther contain components such as a buffer substance, a complexingagent, an antifoaming agent, an organic solvent, a corrosion inhibitor,a dye, an antisludge agent, a dissolution preventing agent such as anon-ionic surfactant, an anionic, cationic or amphoteric surfactantand/or a hydrotropic agent as known in the art. The developer mayfurther contain a polyhydroxyl compound such as e.g. sorbitol,preferably in a concentration of at least 40 g/l, and also apolyethylene oxide containing compound such as e.g. Supronic B25,commercially available from RHODIA, preferably in a concentration of atmost 0.15 g/l; this may be combined with mechanical rubbing, e.g. byusing a rotating brush. During development, any water-soluble protectivelayer present is also removed. In a preferred embodiment, the developeris substantially free of silicates e.g. alkali metal silicates or alkalimetal metasilicates.

More details concerning the development step can be found in for exampleEP 2 263 874, US 2010/0047723 and WO/2004071767.

The development step may be followed by a rinsing step and/or a gummingstep. The gumming step involves post-treatment of the lithographicprinting plate with a gum solution. A gum solution is typically anaqueous liquid which comprises one or more surface protective compoundsthat are capable of protecting the lithographic image of a printingplate against contamination or damaging. Suitable examples of suchcompounds are film-forming hydrophilic polymers or surfactants. Asuitable gum solution which can be used after the development step isdescribed in for example EP 1 342 568 and WO 2005/111727. The plateprecursor can, if required, be further post-treated with a suitablecorrecting agent or preservative as known in the art.

To increase the resistance of the finished printing plate and hence toextend its press life capability the layer can be briefly heated toelevated temperatures (“baking”). The plate can be dried before bakingor is dried during the baking process itself. During the baking step,the plate can be heated at a temperature which is higher than the glasstransition temperature of the heat-sensitive coating, e.g. between 100°C. and 230° C. for a period of 40 seconds to 5 minutes. Baking can bedone in conventional hot air ovens or by irradiation with lamps emittingin the infrared or ultraviolet spectrum. As a result of this bakingstep, the resistance of the printing plate to plate cleaners, correctionagents and UV-curable printing inks increases. Such a thermalpost-treatment is described, inter alia, in DE 1,447,963 and GB1,154,749.

The heat and/or light sensitive printing plates can be used forconventional, so-called wet offset printing, in which ink and an aqueousdampening liquid are supplied to the plate. Another suitable printingmethod uses so-called single-fluid ink without a dampening liquid.Suitable single-fluid inks have been described in U.S. Pat. No.4,045,232; U.S. Pat. No. 4,981,517 and U.S. Pat. No. 6,140,392. In amost preferred embodiment, the single-fluid ink comprises an ink phase,also called the hydrophobic or oleophilic phase, and a polyol phase asdescribed in WO 00/32705.

Examples Synthesis of Inventive IR-Resins 1 to 3 and Comparative Resin 1

The structural formulae shown below indicate the monomer composition ofthe prepared resins but the sequence of the moieties is for illustrationonly.

Unless otherwise specified, all compounds and solvents used in theExamples are readily available from fine chemical suppliers such asAcros or Aldrich.

Test Methods LC-MS Analysis Method 1

The LC-MS analysis according to method 1 was done on a HP 1100 EsquireLC, using an Altima HP C18 AQ column (150×3, 5 μm), operating at a flowrate of 0.5 ml/min and at 40° C. A gradient elution was used, withwater+0.1% formic acid as eluent A and acetonitrile+0.1% formic acid aseluent B. The gradient according to the following Table was used.

Time % B 0 20 7 100 17 100 17.1 20 20 20

ESI ionisation was used in combination with a combibron detector. 5 μlof a solution of 2 mg of each compound in 10 ml acetonitrile wasinjected.

Method 2

The LC-MS analysis according to method 2 was done on a HP 1100 EsquireLC, using an Altima HP C18 AQ column (150×3, 5 μm), operating at a flowrate of 0.5 ml/min and at 40° C. A gradient elution was used, H₂O/MeOH9/1 containing 10 mmol NH₄OAc as eluent A and MeOH containing 10 mmolNH₄OAc as eluent B. The gradient according to the following Table wasused.

Time % B 0 0 12 100 17 100 18 0 20 0

ESI ionisation was used in combination with a combibron detector. 5 μlof a solution of 2 mg of each compound in 10 ml acetonitrile wasinjected.

¹H NMR Analysis

A Varian Unity Inova spectrometer was used, using DMSO d6 as solvent at25° C. with DMSO d5 (2.50 ppm) as internal reference at a spectrometerfrequency of 400 MHz.

Synthesis of Comparative Resin 1

Experimental Procedure:

13.6 g of an ethylene vinyl alcohol copolymer (27 mol % ethylene, EVALSP521 B, supplied by Kuraray) was dissolved in 50 g dimethyl acetamideat 85° C. 0.3 g (3.13 mmol) methane sulfonic acid in 5.6 g dimethylacetamide was added and the mixture was stirred for 10 minutes at 85° C.12.2 g (0.1 mol) salicylic aldehyde in 11.3 g dimethyl acetamide wasadded slowly while keeping the reaction temperature at 80° C. Thereaction was allowed to continue for 1 hour at 80° C. 11.1 g (0.105 mol)trimethyl orthoformate in 5.6 g dimethyl acetamide was added and thereaction was allowed to continue for 90 minutes at 80° C. 0.92 g (3.13mmol) quadrol (CASRN102-60-3) in 7 g dimethyl acetamide was added andthe reaction mixture was stirred for 10 minutes. The reaction mixturewas diluted with 90 ml 1-methoxy-2-propanol and cooled down to roomtemperature. The reaction mixture was further diluted with 100 ml1-methoxy-2-propanol. The mixture was slowly added to 1 l water toprecipitate comparative resin 1. Comparative resin 1 was isolated byfiltration and treated with a mixture of 400 ml water en 100 ml1-methoxy-2-propanol for 16 hours. Comparative resin 1 was isolated byfiltration and dried. 21 g of comparative resin 1 was isolated.

Comparative resin 1 was analyzed using ¹H-NMR spectroscopy. (20 mg ofthe polymer was dissolved in DMSO-d6: the aromatic protons of thepolymer bound phenolic fragments:

6.75 ppm (2H), 7.11 ppm (1H), 7.32 ppm (1H), the acetal protons: 5.70ppm and 5.99 ppm (together 1H), the phenolic proton: 9.30 ppm (1H)).

Synthesis of Inventive IR-Resin 1

1. Derivatisation of poly(ethylene-co-vinylalcohol) with3-hydroxy-benzaldehyde

Experimental Procedure:

279.8 g of an ethylene vinyl alcohol copolymer (29 mol % ethylenesupplied by Aldrich) was dissolved in 1000 g dimethyl acetamide at 100°C. The reaction mixture was cooled to 90° C. A solution of 6 g (62.5mmol) methane sulfonic acid in 75 g dimethyl acetamide was added and themixture was stirred for 10 minutes. A solution of 244.2 g (2 mol)3-hydroxy-benzaldehyde in 200 g dimethyl acetamide was added over 30minutes, while keeping the temperature at 90° C. The reaction wasallowed to continue for 2 hours at 90° C. A solution of 222.8 g (2.1mol) trimethyl orthoformate in 112.5 g dimethyl acetamide was added andthe reaction was allowed to continue at 80° C. for 16 hours. A solutionof 18.3 g quadrol (CASRN102-60-3) in 112.5 dimethyl acetamide was addedand the reaction mixture was stirred for 10 minutes. The reactionmixture was diluted with 1800 1-methoxy-2-propanol and cooled down toroom temperature. The mixture was further diluted with 6000 g1-methoxy-2-propanol and the polymer was precipitated in 30 l water. Thepolymer was isolated by filtration and washed with a mixture of 4 lwater and 1 l 1-methoxy-2-propanol. The polymer was treated with amixture of 5 l water and 1 l 1-methoxy-2-propanol, isolated byfiltration and dried. 450 g of the polymer was isolated.

2. Functionalisation with IR-Dye 1

5.7 g of the 3-hydroxy-benzaldehyde derivatised resin was dissolved in28.5 g dimethyl formamide at 65° C. 20 mg (0.5 mmol) NaH (60% in mineraloil) was added and the reaction was allowed to continue for 30 minutesat 65° C. A solution of 0.39 g (0.5 mmol) of IR-dye 1 (supplied by FEWChemicals) in 10 g dimethyl formamide was added and the reaction wasallowed to continue for 2 hours at 65° C. The reaction mixture wasallowed to cool down to room temperature and the reaction mixture wasdiluted with 105 g 1-methoxy-2-propanol. The mixture was added to 420 gwater. The mixture was stirred for 1 hour. IR-resin 1 was isolated byfiltration, washed with water and dried. 4.8 g of Inventive IR-resin 1was isolated. Inventive IR-resin 1 was characterized using TLC-analysis(on Silicagel 60 F254, supplied by Merck, eluent methylenechloride/methanol 90/10, no residual IR dye detectable at R_(f)=0.5) andUV-VIS-spectroscopy (0.013 w % in dimethyl acetamide:λ_(max):825 nm).

Synthesis of Inventive IR-Resin 2

1. Derivatisation of poly(ethylene-co-vinylalcohol) with4-hydroxy-benzaldehyde

43.5 g EVAL SP521B (supplied by Kuraray) was dissolved in 200 g dimethylformamide at 120° C. The mixture was allowed to cool down to 80° C. 0.96g (10 mmol) methane sulfonic acid, dissolved in 12 g dimethyl formamidewas added, followed by the addition of 39.1 g (0.32 mol)4-hydroxybenzaldehyde, dissolved in 24 g dimethyl formamide. Thereaction was allowed to continue for 45 minutes at 82° C. A solution of37.5 g (0.36 mol) 2,2-dimethoxypropane in 22 g dimethyl formamide wasadded while keeping the temperature at 82° C. The reaction was allowedto continue for one hour at 82° C. A solution of 2.9 g (10 mmol) Quadrol(CASRN102-60-3) in 8 g dimethyl formamide was added and the mixture wasallowed to cool down to room temperature. The mixture was diluted with1300 g 1-methoxy-2-propanol and the polymer was precipitated in 13 lwater. The polymer was isolated by filtration, treated with a mixture of4.3 l water and 860 ml 1-methoxy-2-propanol, isolated by filtration,washed twice with a mixture of 2 l water and 200 1-methoxy-2-propanoland dried. 51 g of the 4-hydroxybenzaldehyde functionalized resin wasisolated.

2. Functionalisation with IR-dye 1

5.7 g of the 4-hydroxy-benzaldehyde derivatised resin was dissolved in28.5 g dimethyl formamide at 65° C. 20 mg (0.5 mmol) NaH (60% in mineraloil) was added and the reaction was allowed to continue for 30 minutesat 65° C. A solution of 0.39 g (0.5 mmol) of IR-dye 1 (supplied by FEWChemicals) in 10 g dimethyl formamide was added and the reaction wasallowed to continue for 2 hours at 65° C. The reaction mixture wasallowed to cool down to room temperature and Inventive IR-resin 2 wasprecipitated in 500 ml water. The mixture was stirred for one hourfollowed by the addition of 75 ml ethanol and stirring over night.Inventive IR-resin 2 was isolated by filtration, washed with water anddried. 2.7 g of Inventive IR-resin 2 was isolated. Inventive IR-resin 2was characterized using TLC-analysis (on Silicagel 60 F254, supplied byMerck, eluent methylene chloride/methanol 90/10, no residual IR dyedetectable at R_(f)=0.5) and UV-VIS-spectroscopy (0.013 w % in dimethylacetamide:λ_(max):813 nm).

Synthesis of Inventive IR-Resin 3

1. Derivatisation of poly(ethylene-co-vinylalcohol) with salicaldehyde

Experimental Procedure:

13.6 g of EVAL SP521 B (supplied by Kuraray) was dissolved in 50 gdimethyl acetamide at 85° C. 0.3 g (3.13 mmol) methane sulfonic acid in5.6 g dimethyl acetamide was added and the mixture was stirred for 10minutes at 85° C. 12.2 g (0.1 mol) salicylic aldehyde in 11.3 g dimethylacetamide was added slowly while keeping the reaction temperature at 80°C. The reaction was allowed to continue for 1 hour at 80° C. 11.1 g(0.105 mol) trimethyl orthoformate in 5.6 g dimethyl acetamide was addedand the reaction was allowed to continue for 90 minutes at 80° C. 0.92 g(3.13 mmol) quadrol (CASRN102-60-3) in 7 g dimethyl acetamide was addedand the reaction mixture was stirred for 10 minutes. The reactionmixture was diluted with 90 ml 1-methoxy-2-propanol and cooled down toroom temperature. The reaction mixture was further diluted with 100 ml1-methoxy-2-propanol. The mixture was slowly added to 1 l water toprecipitate the polymer. The polymer was isolated by filtration andtreated with a mixture of 400 ml water en 100 ml 1-methoxy-2-propanolfor 16 hours. The polymer was isolated by filtration and dried. 21 g ofintermediate polymer was isolated.

2. Functionalisation with IR-Dye 1

5.2 g of the 2-hydroxy-benzaldehyde derivatised resin was dissolved in28.5 g dimethyl formamide at 65° C. 16 mg (0.4 mmol) NaH (60% in mineraloil) was added and the reaction was allowed to continue for 30 minutesat 65° C. A solution of 0.31 g (0.4 mmol) of IR-dye 1 (supplied by FEWChemicals) in 10 g dimethyl formamide was added and the reaction wasallowed to continue for 2 hours at 65° C. The reaction mixture wasallowed to cool down to room temperature. The reaction mixture wasdiluted with 50 g ethanol and Inventive IR-resin 3 was precipitated in600 g water. Inventive IR-resin 3 was isolated by filtration and dried.4.2 g of Inventive IR-resin 3 was isolated. Inventive IR-resin 3 wascharacterized using TLC-analysis (on Silicagel 60 F254, supplied byMerck, eluent methylene chloride/methanol 90/10, no residual IR dyedetectable at R_(f)=0.5) and UV-VIS-spectroscopy (0.013 w % in dimethylacetamide:λ_(max):812 nm).

Preparation of the Lithographic Supports Preparation of the LithographicSupport S-01

A 0.3 mm thick aluminum foil was degreased by spraying with an aqueoussolution containing 34 g/l NaOH at 70° C. for 6 seconds and rinsed withdemineralised water for 3.6 seconds. The foil was then electrochemicallygrained during 8 seconds using an alternating current in an aqueoussolution containing 15 g/l HCl, 15 g/l SO₄ ²⁻ ions and 5 g/l Al³⁺ ionsat a temperature of 37° C. and a current density of about 100 A/dm²(charge density of about 800 C/dm²). Afterwards, the aluminum foil wasdesmutted by etching with an aqueous solution containing 6.5 g/l ofsodium hydroxide at 35° C. for 5 seconds and rinsed with demineralisedwater for 4 seconds. The foil was subsequently subjected to anodicoxidation during 10 seconds in an aqueous solution containing 145 g/l ofsulfuric acid at a temperature of 57° C. and an anodic charge of 250C/dm², then washed with demineralised water for 7 seconds and dried at120° C. for 7 seconds.

The lithographic support was post treated by spraying, onto the abovedescribed support a post treatment solution containing 2.2 g/lpolyvinylphosphonic acid (PVPA) for 4 seconds at 70° C., rinsed withdemineralised water for 3.5 seconds and dried at 120° C. for 7 seconds.

The support thus obtained was characterised by a surface roughness R_(a)of 0.45-0.50 μm (measured with interferometer WYKO NT1100™ Opticalprofiling system) and had an anodic weight of about 3.0 g/m²(gravimetric analysis).

Preparation of Printing Plate Precursors PPP-01 to PPP-07 1. FirstCoating Layer

A first coating solution (Table 1) was applied on the aluminum substrateS-01 at a wet coating thickness of 26 μm. After coating, this firstlayer was dried at 100° C. for 1 minute.

TABLE 1 first coating solution. Composition coating solution % wtDowanol PM(1) 21.23 THF 58.38 Binder (2) 13.69 Crystal Violet(3)  5.02Contrast dye FEW S0944 (4)  1.26 Tegoglide 410(5)  0.42 (1)Propyleneglycol-monomethylether(1-methoxy-2-propanol) commerciallyavailable from Dow Chemical Company; (2) Polysulfonacrylamide (65 mol %sulfonamide/35 mol % N-phenyl-acrylamide)

(3) 1 wt % solution of Crystal Violet in Dowanol PM; Crystal Violet iscommercially available from Ciba-Geigy GnbH.; (4) Cyanine dyecommercially available from FEW Chemicals GmbH.; (5) 1 wt % solution ofTegoglide 410 in Downaol PM; Tegoglide 410 is a copolymer ofpolysiloxane and poly(alkylene oxide), commercially available from TegoChemi Service GmbH.

2. Second Coating Solution

A second coating solution (Table 2) was subsequently coated on theprevious layer (wet coating thickness=26 μm) resulting in printing plateprecursors PPP-01 to PPP-07. The solution was prepared by theingredients given in Table 2 in a 50/50 mixture of methyl-ethylketon(MEK) and dowanol PM®. After coating, this second layer was dried at100° C. for 1 minute.

TABLE 2 Second coating solution. Composition coating solution* mg/m²Resin (1) 436.4 Tetrahydrophtalic acid anhydride 35.0 Alnovol SPN402(44.3 wt %) 100.0 Resole binder (2) Megaface F-253 (3) 3.0 IR-dye 1 (4)Variable, see Table 3 Crystal Violet (1 wt %) (5) 7.5 Total dry coatingweight 581.8 *active ingredients in the coating (1) Comparative resin 1,Inventive IR-resin 1, Inventive IR-resin 2 or Inventive IR-resin 3 asdescribed above; (2) Alnovol SPN402 is a 44.3% wt. solution of novolacresin in Dowanol PM commercially available from Clariant GmbH; (3)Fluorinated acrylic copolymer commercially available from Dainipon Inkand Chemicals; (4) IR absorbing cyanine dye, commercially available fromFEW CHEMICALS GmbH., with the chemical structure IR-dye 1 (see above);(5) 1% wt solution of Crystal Violet in Dowanol PM commerciallyavailable from Ciba-Geigy GmbH.

TABLE 3 printing plates PP-01 to PP-07 Conc. of Conc. Com- non of para-bonded bonded Printing tive Inventive Inventive Inventive IR dye IR dye*Plate Resin 1 IR-Resin 1 IR-Resin 2 IR-Resin 3 mg/m² mg/m² PP-01 X — — —20 — PP-02 — X — — — 31.8 PP-03 — — X — — 15.8 PP-04 — — — X — 27.9PP-05 X — — 31.8 — PP-06 X — — — 15.8 — PP-07 X — — — 27.9 — *100%bonded IR dye

Exposure

The printing plate precursor was image-wise exposed at a range of energydensities with a Creo Trendsetter, a platesetter having a 20 W infraredlaser head (830 nm), operating at 140 rpm and 2400 dpi, commerciallyavailable from Eastman Kodak Corp. The image had a 50% dot coverage andconsisted of a 10 μm×10 μm checkerboard pattern.

The “right exposure” (RE) sensitivity was determined and is defined asthe energy density value (mJ/cm²) at which the 1×1 checkerboard patternon the plate after processing has the same density as the 8×8checkerboard pattern. The density was measured with a Gretag-MacBethD19C densitometer, commercially available from GretagMacbeth AG. Theautomatic colour filter setting was used.

Development

The exposed precursors were treated with a developing solution DEV-01 bydipping (see below). The developing solution is water-based(demineralized water) and the formulation is given in Table 4 below.

Procedure of the Dip Processing

200 ml of the developer in a cylindrical container is placed in anincubator at 25° C. Subsequently, the exposed printing plate precursoris brought into the container including the developer (developertemperature=25° C.) for a pre-defined time (developer dwell time=25seconds) and then thoroughly rinsed with water. Printing plates 01 toPP-07 were obtained.

Dev-01: the formulation of DEV-01 is presented in Table 4 below. The pHis 12.9 and the conductivity is 82 mS/cm.

TABLE 4 Composition of DEV-01 Active ingredients in DEV-01 IngredientDEV-01 (1) g/l Sodium hydroxide (2) 2.3 Sodium metasilicate 66  pentahydrate (3) LiCl 4   Akypo RLM 45CA (4)  3.68 Sodiumsilicate 9.9Na₂O + SiO₂ Briquest 543-25S (5) 1.8 Ralufon DCH (6) 3.7 Preventol R50(7) 1.0 Crodateric CYAP (8) 5   SAG220 (9) 0.1 (1) The pH of DEV-01 is12.9 and the conductivity 82 mS/cm +/−0.1 mS/cm (measured at 20° C.).The ingredients are added to demineralized water (total 1 1); (2) 50 wt.% solution of NaOH in water; (3) metasilicate commercially availablefrom Silmaco NV; (4) 90 wt. % alcohol ether carboxylate surfactantsolution in water, commercially available from Kao Chemicals GmbH; (5)25 wt. % solution of the following compound, commercially available fromRhodia Ltd.:

(6) 50 wt. % of N,N-dimethyl-N-coco-N-(3-sulfopropyl) ammonium betainein water, commercially available from Raschig GmbH:

(7) 50 wt. % solution in water of Preventol R50, commercially availablefrom Bayer AG.; (8) sodium caprylamphopropionate, commercially availabefrom Croda Chemicals Europe Ltd.; (9) SAG220 Anti-Foam Emulsion,polydimethylsiloxane emulsion in water (20 wt % active material),commercially available from Momentive Performance Materials Inc..

Results Sensitivity

The RE sensitivity, determined as described above, obtained for theprinting plate precursors according to the present invention, i.e. theprinting plate precursors including the Inventive IR-resins 1 to 3, aresimilar to the sensitivity of the comparative printing plate precursorincluding Comparative resin 1.

Ablation

The ablation behaviour of the printing plate precursors PPP-01 to PPP-07was tested according to the ablation test method as described below. Theresults of the ablation test are given in Table 5 below.

Ablation Test Method

In a first step, ablation dust is collected via the Fast FilterCollection (FFC) method. Subsequently, the Total Organic Carbon (TOC)measurement provides an accurate value of weight of the released soliddust per plate surface (e.g. mg carbon/m²).

Fast Filter Collection

The Fast Filter Collection (FFC) method is performed on the CreoTrendsetter, a platesetter having a 20 W infrared laser head (830 nm),operating at 140 rpm and 2400 dpi, commercially available from EastmanKodak Corp.

A filter (Pallflex™ Membrame Filter Tissu; Quartz 47 mm; rec. no. 7202)is placed between the laser head and the vacuum cleaner, directly afterthe laser head. The filter is blocked between a grid and a support. Asurface area of the plate of about 4000 cm² is exposed and the dust iscollected on 11 cm² of filter.

One measurement lasts about 5 to 10 minutes. Subsequently, the level ofablation is quantified by means of the Total Organic Carbon (TOC)measurement.

Total Organic Carbon (TOC) Measurement

TOC analysis is a quantitative method providing a total weight of allorganic carbon atoms present in the sample obtained by the FFC method.The amount of carbon atoms which were released during the exposure stepdue to the ablation phenomenon—i.e. mg carbon/m²—is obtained and givesan idea about the degree of ablation.

More details concerning this measurement can be found in the followingstandards:

ISO NBN EN 15936/2012: Sludge, treated bio-waste, soil andwaste—Determination of total organic carbon (TOC) by dry combustion.

NBN EN 13137/2001: Characterization of waste—Determination of totalorganic carbon (TOC) in waste, sludges and sediments.

Results

The results of the ablation test are given in Table 5 below.

TABLE 5 Ablation results Conc. of Conc. of Level of non-bonded bondedablation Printing IR dye IR dye mg C/m² at Plate mg/m² mg/m² 150 mJ/cm²PP-01 20  — 0.23 comparative PP-02 — 31.8 <0.1 inventive PP-03 — 15.8<0.1 inventive PP-04 — 27.9 <0.1 inventive PP-05 31.8 — 0.23 comparativePP-06 15.8 — 0.18 comparative PP-07 27.9 — 0.27 comparative

The ablation results show that there is a clear difference between theprinting plates with bonded IR-dye compared to the printing plates witha similar amount of free IR-dye. The amount of dust collected on thefilter is reduced with more than 50%.

1-10. (canceled)
 11. A copolymer comprising: a plurality of ethylenicmoieties A having a structure according to the formula:

wherein R² and R³ independently represent hydrogen, a halogen, anoptionally substituted linear, branched, or cyclic alk(en)yl group, oran optionally substituted aromatic or heteroaromatic group; a pluralityof acetal moieties B having a structure according to the formula:

 wherein L¹ is a divalent linking group; X=0 or 1; R¹ represents anoptionally substituted aromatic or heteroaromatic group including atleast one hydroxyl group; and a plurality of acetal moieties C and/or aplurality of acetal moieties D that include a structural moietyincluding a chromophoric group having a main absorption in the infraredregion.
 12. The copolymer according to claim 11, wherein the pluralityof acetal moieties C and/or the plurality of acetal moieties D have astructure according to the formulae:

wherein L² and L³ independently represent a divalent linking group; Yand z independently represent 0 or 1; and R⁴ and R⁵ independentlyrepresent a structural moiety including a chromophoric group having amain absorption in the infrared region.
 13. The copolymer according toclaim 11, wherein the plurality of acetal moieties C have a structureaccording to the formula:

wherein R6 represents a structural moiety including a chromophoric grouphaving a main absorption in the infrared region and a bond to the centerof the aromatic ring indicates that any of the hydrogen atoms of thearomatic ring may be substituted by —O—R6.
 14. The copolymer accordingto claim 11, wherein the chromophoric group has a structure according tothe formula:

wherein T and T′ independently represent one or more substituents or anannulated ring; Z and Z′ independently represent —O—, —S—,—CR^(e)R^(f)—, or —CH═CH— and wherein R^(e) and R^(f) independentlyrepresent an optionally substituted alkyl or aryl group; R^(z) andR^(z′) independently represent an optionally substituted alkyl group;R^(b) and R^(c) independently represent a hydrogen atom, an optionallysubstituted alkyl group, or atoms necessary to form an optionallysubstituted ring structure; R^(a) and R^(d) independently represent ahydrogen atom or an optionally substituted alkyl group; R^(z) and R^(a)or R^(d) and R^(z′) may represent atoms necessary to form an optionallysubstituted 5- or 6-membered ring; X⁻ renders the chromophoric groupneutral; and * denotes a linking position.
 15. The copolymer accordingto claim 12, wherein the copolymer comprises the plurality of acetalmoieties C.
 16. The copolymer according to claim 11, wherein R² and R³represent hydrogen.
 17. The copolymer according to claim 11, which isrepresented by the formula:

wherein R⁷ is an optionally substituted alkyl group; m is in a range of10 to 55 mol %; n is in a range of 15 to 60 mol %; o is in a range of 10to 60 mol %; p is in a range of 0 to 10 mol %; and q is in a range of0.25 to 25 mol %.
 18. A positive-working lithographic printing plateprecursor comprising: a support including a hydrophilic surface or whichis provided with a hydrophilic layer; and a heat- and/or light-sensitivecoating provided on the support; wherein the coating includes thecopolymer as defined in claim
 11. 19. A method of making a lithographicprinting plate precursor comprising the steps of: providing a supportwith a hydrophilic surface or with a hydrophilic layer; applying acoating including the copolymer as defined in claim 11 on the support oron the hydrophilic layer; and drying the precursor.
 20. A method ofmaking a lithographic printing plate comprising the steps of: providinga lithographic printing plate precursor according to claim 18;image-wise exposing the lithographic printing plate precursor with heatand/or light; and developing the lithographic printing plate precursorby treating the lithographic printing plate precursor with a developingsolution to remove exposed areas of the coating from the support or thehydrophilic layer.